In this work, an innovative colorimetric assay method for the determination of carcinoembryonic antigen is developed with aptamer probes utilized as recognition element. DNA hybridization chain reaction is used as signal amplification technique, and peroxidase-mimicking hemin/G-quadruplex-assisted catalytic oxidation of 2,2'azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) is deployed as signal reporting mechanism. The detection principle was firstly verified by using gel electrophoresis analysis and absorbance measurements. After condition optimization, a detection limit was theoretically determined as 24.8 ng/ml. Furthermore, the method exhibited good selectivity and satisfactory recovery rates (92.2%-108.6%) in serum samples. Moreover, the sensing scheme is easily extended for the detection of other analytes via similar target-aptamer recognition principle. To sum up, this is an enzyme-and label-free, cost-effective yet signal-amplifiable assay scheme for the determination of tumor markers with promising simplicity and selectivity, practical utility, and potential universality.

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Biosensors always respond to the targets of interest in a specific manner, employing biological or bio-mimic recognition elements such as antibodies and aptamers. Inspired by target recognition in nature, an aptamer-mediated, gold nanoparticle-based sensing approach is developed in this work for effective determination of malathion. The sensing system consists of negatively charged aptamer probes, and polycationic proteins, protamine, as well as exceptional colorimetric nanoprobes, barely gold nanoparticles (AuNPs). Protamine molecules bound to aptamer probes hinder the aggregation of AuNPs, while no such inhibition is maintained when aptamer-specific malathion is introduced into the solution, thus leading to the solution colour change from red to blue observable by the naked eye. The assay is accomplished via a mix-and-measure step within 40 min with a detection limit as low as 1.48 μg/L (3σ/s rule). The assay method also exhibits high selectivity and good applicability for the quantification of malathion in tap water with recovery rates of 98.9%–109.4%. Additionally, the good detection accuracy is also confirmed by the high-performance liquid chromatography method. Therefore, the non-enzymatic, label- and device-free characteristics make it a robust tool for malathion assay in agricultural, environmental, and medical fields.